The objective of the study is to assess the validity of a new hypothesis of inert gas narcosis. This hypothesis suggests that the anesthetic potency of metabolically inert gases is due to their effect on the "free volume" of a bulk lipid phase, possibly in the cell membrane. More specifically, narcosis occurs when the inert gas dissolved in the lipid phase causes the free volume to exceed a specific threshold value. The new hypothesis is expressed in quantitative terms and appears to be in good agreement with experimental data from the literature for both pure gases and gas mixtures. The present work is directed toward the measurement of free-volume parameters which are required for a more rigorous test of the hypothesis.